Optical fibers are used for data transmission and sensor applications; types of optical fibers are optical glass fibers made of glass such as silica, and plastic optical fibers made of plastics (hereinafter referred to as “POF”).
POFs are structured mainly to have a core made of highly transparent resin such as polymethyl methacrylate and, around the core, a resin with a refractive index lower than that of the resin of the core. Compared with glass optical fibers, the transmission distance of POFs is shorter, but POFs have advantages such as easier handling, simplified formation of connectors, lightweight and inexpensive material, and diameters that can be set greater. Thus, POFs are used in diversified applications such as illumination, sensors and communication systems, and the production of POFs is on the rise.
When optical fibers are used, it is rare to use them alone, except for illumination purposes. Generally, optical fibers are coated with resins to form optical fiber cables so that properties such as mechanical strength, heat resistance and flame retardancy are provided for the cables.
Regulations on flame retardant plastics have become stricter recently. When a POF is used in plenum spaces such as in a building or condominium, high flame retardancy properties are also required for the POF. To satisfy such a requirement, various types of optical fiber cables have been proposed.
For example, Patent Publication 1 describes that when a halogen-free phosphoric ester-based flame retardant and a hindered amine-based stabilizer are added to a polypropylene resin, an optical fiber cable is obtained which exhibits flame retardancy to a degree that passes flame testing specified in DIN 72551-5.
Patent Publications 2 and 3 disclose that flame retardancy properties are provided for POF cables by using a chlorinated polyethylene resin and a vinyl chloride resin (or a composition containing a vinyl chloride resin) respectively as the resin to coat the POF.
Patent Publications 4 and 5 disclose that flame retardancy properties are provided for POF cables by using a coating material prepared by adding a flame retardant such as metal hydroxide to a polyethylene resin.
In addition, Patent Publication 6 describes a fiber optic cord formed by coating a polymer alloy containing polyphenylene ether on an optical fiber formed using silica glass as a main component.